IRC Stair & Guard Rules: Riser, Tread, Handrail, Guards

The requirement

The IRC sets a residential stair with a handful of numbers you can measure with a tape. The two that shape every step are the riser and the tread.

Riser — how tall each step is. The IRC caps it at 7¾ in (196 mm). Go taller and the step is too big to climb safely, so you add a step to bring each one down. Every riser in a flight must be near-equal, varying no more than 3/8 in top to bottom (R311.7.5.1).
Tread depth (the going) — how deep each step is, measured nosing to nosing (front edge of one step to the front edge of the next). The IRC minimum is 10 in (254 mm) (R311.7.5.2).

Then three more that keep the stair usable:

Dimension	IRC minimum
Riser height	max 7¾ in (196 mm)
Tread depth	min 10 in (254 mm)
Headroom	min 6 ft 8 in (2032 mm) (R311.7.2)
Clear width	min 36 in (914 mm) (R311.7.1)
Handrail height	34–38 in (864–965 mm) above the nosing line (R311.7.8)

A handrail is required on any flight with 4 or more risers. It runs 34 to 38 in above the line drawn across the stair nosings.

IRC 2021 · R311.7

Every step in a flight must be the same height and the same depth. The IRC only allows a tiny difference, because one odd step is where people trip.

Guards & barriers

A guard is the barrier that stops someone falling off an open edge. The IRC ties it to the height of the drop, not to the stair itself.

Rule	IRC figure
Guard height	min 36 in (914 mm) (R312.1)
Fall-height trigger	required where a walking surface is more than 30 in (762 mm) above the floor or grade below, within 36 in horizontally
Open-side stair guard	may sit 34–38 in where it doubles as the handrail
Opening — general	a 4 in (102 mm) sphere must not pass through (R312.1.3)
Opening — open side of a stair	up to 4⅜ in
Opening — riser/tread/rail triangle	up to 6 in

So: if you can fall more than 30 in, you need a guard at least 36 in high. The 4 in sphere rule means the gaps in it can’t be wide enough to let a small child’s head through — with a slightly larger allowance at the open side of the stair and in the triangle formed by the riser, tread and bottom rail.

Work it out on site

Say your floor-to-floor height is 105 in and you want an even set of steps.

Pick how many risers. 105 ÷ 7¾ (the tallest a riser can be) = 13.5. You can’t have half a step, so round up to 14 risers. 105 ÷ 14 = 7.5 in per riser — under the 7¾ limit. Good.
Set the tread. Use a 10 in tread or deeper, so it clears the minimum.
Check headroom and width as you lay it out — 6 ft 8 in of clear height above the pitch, 36 in of clear width.

If 105 ÷ your riser count lands over 7¾, add a riser and divide again. Keep every step equal. (These are example numbers — plug your real floor-to-floor height into the calculator.)

Do it in 5 seconds

US building codes: the IRC, state by state — how the model code gets adopted and amended, and why you check your local edition first.
NCC stair requirements (Australia) — the same stair rules for readers building down under.

Sources

IRC 2021, Section R311.7 — Stairways (riser, tread, headroom, width, handrail) and Section R312 — Guards (guard height, fall trigger, openings). Read the code at codes.iccsafe.org.
Adoption & edition caveat — read this first. The IRC is a model code. It has no force until your state and/or town adopts it, almost always with local amendments. Editions in force are a patchwork — many places are still on IRC 2018 or 2015 — and California (CRC), Wisconsin, New York City and Chicago run their own codes. The figures above are the base IRC 2021 (stable across 2015–2024), but the enforceable number is the adopted-and-amended edition where you build. Confirm the edition and amendments with your local building department before you set out. Footing sizes (R403.1) are not listed here on purpose — they’re table-driven by your soil-bearing and loads, so read your soil/load table, don’t copy a number.

State variations

These states apply requirements that differ from the national provisions for this rule.

California Adopted R312

Current code: California Residential Code (2025)

California requires guards at least 42 in (1067 mm) high — taller than the IRC's 36 in. Stair geometry (riser, tread, headroom) otherwise matches the IRC.

California building codes → Official source → Verified 2026-07-28

Frequently asked questions

What is the maximum riser height for stairs in the US?

Under the IRC, a riser — the up-and-down face of a step — can be no taller than 7¾ in (196 mm). Every riser in the same flight must also be close to equal, within 3/8 in top to bottom. But first check which edition and amendments your state and town adopted, because that is the version that actually applies to your job.

What is the minimum tread depth?

The IRC minimum tread depth — how deep each step is, measured nosing to nosing — is 10 in (254 mm). That's the flat part your foot lands on. As always, confirm the edition your local building department enforces.

Do I need a handrail, and how high?

You need a handrail on any flight with 4 or more risers. It sits 34 to 38 in (864–965 mm) above the line drawn across the stair nosings. Check your adopted edition, since a local amendment can change this.

When is a guard required and how high?

A guard — the barrier that stops a fall off the open side — is required where a walking surface is more than 30 in (762 mm) above the floor or ground below, within 36 in horizontally. Guards must be at least 36 in (914 mm) high. An open-side stair guard that also works as the handrail may sit 34 to 38 in.

Which code edition applies to my job?

That's the whole point: the IRC is a model code with no force until your state and/or town adopts it — almost always with amendments. Many places are still on IRC 2018 or 2015; California, Wisconsin, NYC and Chicago run their own codes. Confirm the adopted-and-amended edition with your local building department before you build.